Visbreaking A Heavy Hydrocarbon Feedstock In A Regenerable Molten Medium

Abstract

Heavy hydrocarbon feed stocks such as atmospheric and vacuum residua, heavy crude oils and the like are converted to predominantly liquid hydrocarbon products by contacting said feed stocks with a stable regenerable molten medium containing a glass-forming oxide such as boron oxide at a temperature in the range of from about 600.degree. to about 1,200.degree. F. Preferably, the stable, regenerable molten medium comprises a glass-forming oxide in combination with an alkaline reagent. The carbonaceous materials such as coke which are formed in the molten medium during the above-described conversion process are gasified by contacting said carbonaceous materials with a gaseous stream containing oxygen such as air, steam, or carbon dioxide at temperatures of from above about the melting point of said medium to about 2,000.degree. F. in order to gasify said carbonaceous materials and thereby regenerate the molten medium. The conversion of a heavy hydrocarbon feed stock by the above-described process reduces the viscosity of the feed stock and thereby produces increased proportions of predominantly liquid hydrocarbon products of the motor fuel range and fuel oils.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of Ser. No. 186,770, filed Oct. 5, 1971 and now abandoned.

Description

FIELD OF THE INVENTION

This invention relates to the conversion of heavy hydrocarbon feedstocks to produce increased proportions of motor fuel range hydrocarbons and fuel oils. More particularly, this invention relates to converting a heavy hydrocarbon feedstock to liquid hydrocarbon products by contacting said feedstock with a molten medium. Still more particularly, this invention relates to the conversion of a heavy hydrocarbon feedstock such as atmospheric and vacuum residua, crude oils and the like, in a stable, regenerable molten medium containing a glass-forming oxide such as boron oxide to produce predominantly liquid hydrocarbon products such as a gas oil and carbonaceous materials, namely coke. The carbonaceous materials formed during the cracking process are gasified by contacting said carbonaceous materials in the molten medium with a gasifying reagent such as air, at elevated temperatures in order to regenerate the melt.

DESCRIPTION OF THE PRIOR ART

Heavy hydrocarbon materials such as atmospheric or vacuum residua, crude oil and the like, are typically subjected to a viscosity-reducing or "visbreaking" treatment at high temperatures and elevated pressures to effectuate by a mild thermal cracking of the feedstock to about 5 to 15 percent gas oil, about 5 to 15 volume percent gasoline, and about 75 to 85 percent heavy fuel oil. The specific temperatures, pressures, and feed rates employed in the visbreaking process depend upon the type of the visbreaker feed. The gas oil formed by such a process represents a feedstock suitable for the production of additional amounts of high quality gasoline by catalytic cracking or, after suitable finishing, an acceptable distillate fuel. Of the products formed in visbreaking, gasoline has the highest and the fuel oil the lowest value. In order to obtain the greatest product realization, it is highly desirable, therefore, to reduce the fuel oil yields to a minimum while simultaneously increasing the gasoline and gas oil yields to a maximum. This may be accomplished by increasing the severity of the thermal cracking treatment, that is, by raising the temperature and/or extending the cracking time.

The conversion of heavy hydrocarbon feedstocks such as residua is relatively difficult in view of their tendency to form coke when subjected to moderately high temperatures. This coke-forming tendency has also limited the industrial application of employing molten heat transfer media in order to effect the hydrocarbon conversion of such feedstocks. The difficulty primarily encountered in employing molten media systems for such conversion processes was the fact that the carbonaceous particles, i.e., coke, produced during the conversion operation were not suspended in the melt, but formed a separate phase which contaminated the liquid and gaseous products. With melts that partially suspended the coke, such as alkali metal halide eutectics, i.e., lithium-potassium chloride, the buildup of such carbonaceous materials in or above the molten medium necessitated additional steps to physically remove the carbonaceous particles from the melt.

It has been suggested that hydrocarbon feedstocks can be cracked in a molten salt of either alkali metal carbonate, alkali metal hydroxide, or a mixture thereof, to form hydrocarbon products containing ethylene and thereafter regenerating the molten salt by intimate contact with oxygen or steam (see U.S. Pat. Nos. 3,553,279 and 3,252,774). Further, in Czechoslovakian Patent 109,952 it is disclosed that various compositions can be employed in the thermal cracking of hydrocarbons.

SUMMARY OF THE INVENTION

It has now been discovered that heavy hydrocarbon feedstocks are converted to predominantly liquid hydrocarbon products by contacting said liquid feedstocks with a molten medium as hereinafter defined, at a temperature in the range of from above about the melting point of said medium to about 1,200.degree.F. for a period of time sufficient to form said liquid products. Thereafter, the carbonaceous materials formed and suspended in the molten medium during the conversion operation are contacted with a gasifying reagent such as a gaseous stream containing elemental or combined oxygen, e.g., air, carbon dioxide, steam, and mixtures thereof, at a temperature in the range from about the melting point of said medium to about 2,000.degree.F. for a period of time in order to regenerate the molten medium.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a flow plan of an integrated cracking/gasification process unit for cracking hydrocarbon feedstocks to predominantly liquid products.

The regenerable molten medium of the instant invention comprises a glass-forming oxide (or oxide precursor), by which is meant an oxide of silicon, germanium, boron, phosphorus, arsenic, antimony, tellurium, selenium, molybdenum, tungsten, bismuth, aluminum, gallium, vanadium, titanium, and mixtures thereof. Preferably, the glass-forming oxides are selected from the group consisting of oxides of boron, phosphorus, vanadium, silicon, tungsten, and molybdenum. An oxide of boron is the most preferred glass-forming material.

The glass-forming oxides are employed in combination with an alkaline reagent, by which term is meant (a) alkali metal (Group IA) oxides, alkali metal hydroxides and mixtures thereof, and (b) alkali metal oxides, alkali metal hydroxides and mixtures thereof in combination with alkaline earth metal (Group IIA) oxides, hydroxides and mixtures thereof. When mixtures of alkali metal compounds and alkaline earth metal compounds are employed, the mixture typically contains a minor proportion of the alkaline earth materials. Alkaline earth oxides and hydroxides have relatively high melting points and are of limited utility in this process wherein the reaction temperatures do not exceed about 1,200.degree.F. The preferred alkali metals are sodium, lithium, potassium, cesium and mixtures thereof. The preferred alkaline earth metal materials are magnesium, calcium, strontium, and barium. The most preferred alkaline reagent comprises one or more alkali metal hydroxides or one or more alkali metal hydroxides in combination with major or minor amounts of one or more alkali metal oxides. Desirably, the molar ratio of alkaline reagent (calculated on the basis of the oxide thereof) to glass forming oxide present in the melt varies in the range of from about 0.01 to about 5, more preferably from about 1.5 to about 3, and most preferably from about 2.2 to about 2.7.

When a gaseous stream containing elemental oxygen, for example air, is employed in order to gasify the carbonaceous materials present in the molten medium of the instant invention, the preferred mole ratio of the alkaline reagent (calculated on the basis of the oxide thereof) to glass-forming oxide in the gasification zone is in the range of from about 0.5 to about 2.5. However, when steam is employed to gasify the carbonaceous materials, the preferred mole ratio of the alkaline reagent (calculated on the basis of the oxide thereof) to glass-forming oxide in the gasification zone is in the range from about 0.5 to about 2.0. When the mole ratio of the alkaline reagent (calculated on the basis of the oxide thereof) to glass-forming oxide is within the above-described preferred ranges, there occurs a significant increase in the gasification rate of the carbonaceous materials suspended in the molten medium of the instant invention; however, the gasification process is operable if the alkaline reagent/glass forming oxide ratio falls outside the preferred ranges.

The advantage of converting a heavy hydrocarbon feedstock in the above-mentioned molten medium, in addition to providing the heat transfer medium for the conversion of the heavy hydrocarbon feedstock to the predominantly liquid hydrocarbon products, lies in the ability of said medium to: (a) suspend the carbonaceous materials formed in situ during the conversion operation uniformly throughout the melt, (b) abstract sulfur from the hydrocarbon materials being treated, and (c) thereafter, upon contact with a gasifying reagent at elevated temperatures to promote the rapid gasification of said carbonaceous materials. Accordingly, the instant invention attains a higher conversion of the heavy hydrocarbon feedstocks to predominantly liquid hydrocarbons than that which is obtainable with more conventional methods such as visbreaking. This is due to the fact that the conversions that are obtained by conventional thermal pyrolysis techniques such as visbreaking are normally quite low in view of the fact that such conversion processes must be carried out at low temperatures. Attempts to conduct such processes at higher temperatures in order to obtain higher conversions are limited by the formation of carbonaceous materials such as coke with accompanying operability problems. Accordingly, the molten medium of the instant invention allows one to conduct such conversion processes at higher temperatures, thereby obtaining higher conversions to the predominantly liquid products in view of the fact that the carbonaceous materials formed during said conversion process may be gasified by contacting said carbonaceous materials with a gasifying reagent, as hereinafter defined.

In addition to promoting the gasification rate of the carbonaceous materials formed during the conversion process, the molten medium of the instant invention offers the additional advantages of significantly lowering the emission of pollutants into the atmosphere by absorbing or reacting with at least a portion of the sulfur and/or sulfur compounds produced during the actual cracking operation and/or during the combustion of carbonaceous material during the gasification phase of the process. The liquid hydrocarbon products formed with the conversion process of the instant invention contain a significantly reduced amount of heavy metals compared to that originally contained in the heavy hydrocarbon feed. Furthermore, the molten medium of the instant invention possesses good thermal conductivity to allow efficient heat transfer and possesses high stability such as to undergo essentially no decomposition to volatile products under the thermal conversion or gasification conditions. Thus, it is evident that these advantageous properties exhibited by the stable, regenerable molten medium of the instant invention offer significant advantages in the thermal cracking of heavy hydrocarbon feedstocks.

The melts may contain other components such as ash constituents, metallic and nonmetallic oxides, sulfides, sulfites, sulfates and various other salts in varying amounts so long as the medium is molten at the hydrocarbon conversion conditions of the instant invention, i.e., less than about 1,200.degree.F., and preferably from about 600.degree. to less than about 1,200.degree.F., and more preferably from about 800.degree. to about 1,100.degree.F. and provided that a sufficient amount of glass-forming oxide is employed to maintain the molten medium in a regenerable condition. One skilled in the art will readily determine the applicable components as well as the stoichiometry of the glass-forming oxides to said components which will be required in order to form the regenerable molten medium as described above. Further, various filler materials, catalysts or promoters may be added to the melt.

Typical examples of stable molten media containing alkali metal oxides in combination with glass-forming oxides that may be employed in the practice of the instant invention are shown in Table I, following. The same melts could be formed from hydroxides.

TABLE I ______________________________________ Molten Glass Composition, Approximate Mixture Mole Ratio Melting Point, .degree.F. ______________________________________ Li.sub.2 O.sup.. K.sub.2 O.sup.. B.sub.2 O.sub.3 0.5/0.5/1 1070 Li.sub.2 O.sup.. Cs.sub.2 O.sup.. B.sub.2 O.sub.3 0.3/0.7/1 1076 K.sub.2 O.sup.. V.sub.2 O.sub.5 0.6/1 734 Li.sub.2 O.sup.. Na.sub.2 O.sup.. WO.sub.3 1.1/1/2.1 917 K.sub.2 O.Li.sub.2 O.MoO.sub.3 0.4/1/1.4 955 Na.sub.2 O.SiO.sub.2.B.sub.2 O.sub.3 0.8/0.8/1 968 Li.sub.2 O.K.sub.2 O.B.sub.2 O.sub.3 1.3/0.7/1 1000 Li.sub.2 O.Na.sub.2 O.B.sub.2 O.sub.3 1.5/0.5/1 940 Na.sub.2 O.P.sub.2 O.sub.5 1.2/1 1026 Li.sub.2 O.Na.sub.2 O.P.sub.2 O.sub.5 0.5/0.5/1 888 Li.sub.2 O.K.sub.2 O.P.sub.2 O.sub.5 0.5/0.5/1 874 Li.sub.2 O.K.sub.2 O.SO.sub.3.P.sub.2 O.sub.5 1.4/0.5/1/1 860 ______________________________________

It is to be understood that although the molten medium of the instant invention is described throughout the specification in terms of the alkaline reagent and the glass-forming oxides, it is clearly within the scope of this invention to employ and define the molten medium of this invention with respect to the compounds, i.e., the salt formed when a glassforming oxide is heated to the molten state in combination with the alkaline reagent. For example, a molten medium consisting of lithium oxide and potassium oxide as the alkaline reagent and boron oxide as the glass-forming oxide in the following mole ratios, 0.53 Li.sub.2 O, 0.47 K.sub.2 O, 1.0 B.sub.2 O.sub.3, can also be expressed in the molten state as a borate, specifically a lithium potassium metaborate on the basis of the following reaction:

0.53 mole Li.sub.2 O + 0.47 mole K.sub.2 O + 1 mole B.sub.2 O.sub.3 .fwdarw. 1.06 LiBO.sub.2 + 0.94 KBO.sub.2

Hence, when a molar excess of the glass-forming oxide (B.sub.2 O.sub.3) is employed, the melt may comprise a glass-forming oxide in combination with an alkali metal borate in accordance with the following reaction:

0.53 Li.sub.2 O + 0.47 K.sub.2 O + 2 B.sub.2 O.sub.3 .fwdarw. 1.06 LiBO.sub.2 + 0.94 KBO.sub.2 + B.sub.2 O.sub.3

Accordingly, it is clearly within the purview of the instant invention to employ as the stable molten medium of this invention a glass-forming oxide, as defined above, in combination with an alkaline reagent or an alkaline reagent salt of the glass-forming oxide employed, e.g., alkali metal borate. It is to be noted that any of the molten glass melts of this invention may be prepared by fusing any combination of raw materials, which upon heating will form a glass-forming oxide either alone or in combination with an alkaline reagent.

Individual regenerable stable molten systems that are most preferred are those obtained when boron oxide or phosphorus pentoxide is employed as the glass-forming oxide. The most preferred melt system of the instant invention comprises boron oxide in combination with a hydroxide of lithium, potassium, sodium and mixtures thereof as the alkaline reagent. The hydroxide may be used in combination with other alkali metal oxide. The most preferred alkaline reagent is a major amount of a mixture of lithium, potassium and sodium hydroxides and a minor amount of alkali metal oxides.

In a process of this invention a wide variety of feedstocks may be converted to produce predominantly liquid hydrocarbon products. Generally, the hydrocarbon feedstocks of the instant invention are heavy hydrocarbon feedstocks such as crude oils, heavy residua, atmospheric and vacuum residua, crude bottoms, pitch, asphalt, other heavy hydrocarbon pitchforming residua, coal, coal tar or distillate, natural tars including mixtures thereof. Preferably, at least a portion of the heavy hydrocarbon feedstocks boils above about 650.degree.F. at atmospheric pressure. Most preferably, the hydrocarbon feedstocks that can be employed in th practice of the instant invention are crude oils, aromatic tars, atmospheric or vacuum residua containing materials boiling above about 650.degree.F. at atmospheric pressure.

While not essential to the reaction, an inert diluent can be employed in order to regulate the hydrocarbon partial pressure in the molten media conversion zone. The inert diluent should normally be employed in a molar ratio from about 1 to about 50 moles of diluent per mole of hydrocarbon feedstock, and more preferably from about 1 to about 10 moles of diluent per mole of hydrocarbon feed. Illustrative, non-limiting examples of the diluents that may be employed in the practice of the instant invention include helium, carbon dioxide, nitrogen, steam, methane, and the like.

As mentioned above, the conversion process of the instant invention results in the formation of predominantly liquid (at atmospheric pressure) hydrocarbon products. The conversion of the above-described heavy hydrocarbon feedstocks results in upgrading said feedstocks, by which is meant that the high percentage, i.e., above 60, and more preferably above 80 weight percent of the material boiling above a temperature of 975.degree.F. (at atmospheric pressure) is converted to lower boiling liquid hydrocarbon products and coke. Such an unexpectedly high conversion to liquid hydrocarbon products by the practice of the instant invention is to be contrasted with the more conventional mild pyrolysis techniques for converting heavy hydrocarbon feedstocks such as visbreaking and hydrovisbreaking which normally result in below about 50 weight percent conversions of materials boiling above about 975.degree.F. Normally, the amount of materials having four carbon atoms and lighter (C.sub.4 .sup.-) formed in accordance with the practice of the instant invention is usually below 10 wt. percent of the total feedstock and the amount of gas oil (boiling between about 430.degree. to 650.degree.F. at atmospheric pressure) formed by the process of this invention is normally in the range of from about 10 to 30 wt. percent of the total feedstock.

In a typical embodiment of this invention, and one which clearly illustrates the effectiveness of the stable, regenerable molten medium as a conversion and gasification medium, a heavy hydrocarbon feedstock having an API gravity of 7.1 and an elemental analysis of 83.1 weight percent carbon; 10.59 weight percent hydrogen, 4.30 weight percent sulfur, 0.50 weight percent nitrogen and a hydrocarbon atomic ratio of 1.517 and having a Conradson carbon residue of 15.0 weight percent and containing 0.0 weight percent materials boiling below 430.degree.F.; 9.8 weight percent materials boiling in the range of from 430.degree. to 650.degree.F.; 35.9 weight percent materials boiling in the range of from 650.degree. to 1,050.degree.F. and 54.3 weight percent materials boiling above about 1,050.degree.F. is processed in a stable, regenerable molten medium in order to convert said feedstream to predominantly liquid hydrocarbon products and carbonaceous materials and thereafter gasifying said carbonaceous materials in order to regenerate the melt system.

The heavy hydrocarbon feedstock is contacted with a molten sodium polyphosphate bed containing 55.1 weight % Na.sub.2 O.sup.. P.sub.2 O.sub.5 ; 30.4 weight % 2Na.sub.2 O.sup.. P.sub.2 O.sub.5 and 14.5 weight % Na.sub.2 SO.sub.4. Alternately, the molten medium may be sprayed into a reactor or trickled down the reactor wall where the hydrocarbon feedstock passes through the reactor. The molten medium can flow either cocurrently or countercurrently to the hydrocarbon flow. The temperature of the molten medium is maintained in the range of from above the melting point of said medium to less than about 1,200.degree.F., and more preferably from about 800.degree. to about 1,100.degree.F. in order to form predominantly liquid hydrocarbon products and carbonaceous materials.

Depending upon the temperature and the specific type of hydrocarbon feedstock, the weight ratio of molten media to hydrocarbon in the reaction zone varies in the range of from 0.1 to 1 to about 100 to 1 and preferably from 5 to 1 to 20 to 1. The reaction may be conducted at pressures ranging from subatmospheric to about 50 atmospheres, preferably from about 1 to about 10 atmospheres. The reaction time is expressed in the amount of time the feedstock is in contact with the melt, i.e., residence time is in the range of from about 0.001 to about 6 hours, and more preferably from about 0.1 to about 3 hours.

After the hydrocarbon feedstock has been converted in the molten medium at the desired temperature and pressure, the hydrocarbon effluent from the reaction zone is cooled to condense and separate liquid products from the gaseous products containing light olefins. The significant advantage of the instant invention is that the carbonaceous materials (coke) which are formed during the conversion process become suspended in the molten medium and can subsequently be gasified by contacting the melt with a gasifying reagent such as a gaseous stream containing free or combined oxygen, i.e., air, steam, carbon dioxide and mixtures thereof, at elevated temperatures in order to rapidly regenerate the stable molten medium. The carbonaceous materials that are formed during the thermal cracking reaction may be generally described as solid particle-like materials having a high carbon content such as those materials normally formed during high temperature pyrolysis of organic compounds.

The term gasification as used herein describes the contacting of the carbonaceous materials in the molten media with a reagent containing elemental or chemically combined oxygen such as air, steam, carbon dioxide, and mixtures thereof. The gasification reaction is carried out at temperatures in the range of from above about the melting point of the molten media up to about 2,000.degree.F. or higher and at a pressure in the range of from subatmospheric to about 100 atmospheres. More preferably, the temperature at which the gasification reaction is carried out is in the range of from about 1,000.degree. to about 1,800.degree.F. and at a pressure in the range of from about 1 to about 10 atmospheres.

Normally, the amount of oxygen which must be present in the gaseous stream containing free or combined oxygen in order to effectuate the gasification of the carbonaceous materials is in the range of from about 1 to about 100 weight percent oxygen, and more preferably from about 10 to about 25 weight percent oxygen. Normally, the gaseous stream containing oxygen is passed through the melt at a rate of from less than about 0.01 w./w./hr. to about 100 w./w./hr. More preferably, the rate at which the gaseous stream is passed through the melt system of the instant invention is in the range of from about 0.01 w./w./hr. to about 10 w./w./hr. Preferably air is employed as the gaseous stream containing oxygen in order to effect a rapid regeneration of the molten medium.

Steam or carbon dioxide, either alone or in admixture with oxygen may also be employed to gasify the carbonaceous materials present in the molten medium of the instant invention. However, as is appreciated in the art, the different gasification reagents mentioned above will each gasify the carbonaceous material at different rates. Generally, the presence of free elemental oxygen in the melt will result in higher gasification rates than with other reagents such as steam or CO.sub.2. Thus, when steam or CO.sub.2 is employed as the gasification reagent, more severe conditions, e.g., higher temperatures and longer residence time, will be required in order to achieve gasification rates equivalent to or higher than when, for example, air or oxygen is employed as the gasification reagent.

The specific gasification rate of the carbonaceous materials in individual stable, regenerable molten media, as defined by the amount of carbonaceous material which is gasified per hour per cubic foot of melt, is dependent upon the temperature at which the gasification process is carried out, as well as the residence time of the oxygen containing gas or steam in the melt, the concentration of carbonaceous material in the melt, and feed rate of oxygen containing gas into the media. As a general rule, the carbon gasification rate increases as the temperature of the melt, concentrations of carbonaceous materials and feed rate of the oxygen-containing gas increase. Preferably, the concentration of carbonaceous materials in the molten medium is maintained in the range of from about 0.1 to about 60 weight percent, and preferably from about 1.0 to about 20 weight percent, in order to effect a rapid gasification thereof. Accordingly, it can be seen that it is advantageous to carry out the gasification reaction process at temperatures above about 1,000.degree.F., and more preferably in the range of from 1,000.degree. to 1,800.degree.F. and at an oxygen gas feed rate of 0.01 to 10 w./w./hr. in the presence of from about 1.0 to about 10 weight percent carbonaceous materials in order to effectuate a rapid gasification of the carbonaceous materials present in the melt. Such a rapid gasification will necessarily result in a rapid regeneration of the melt.

Referring now to the FIGURE, a heavy hydrocarbon residuum fraction, preferably having an initial boiling point (at atmospheric pressure) above about 650.degree.F., is introduced to cracking zone 2 via feed line 1. Within the cracking zone is maintained a molten bed 3 containing an oxide of boron and an alkaline reagent comprising a major amount of a mixture of sodium, potassium and lithium hydroxides in combination with a minor amount of sodium, potassium and lithium oxides. The hydrocarbon feedstock may be passed upwardly through melt 3 by introducing the feed stock at a point below the upper level of the molten media. The temperature of the molten media 3 is maintained below about 1,200.degree.F.

After the hydrocarbon feed stock has been at least partially reduced to lighter products through contact with the hot molten media 3, the resulting cracked products pass overhead from cracking zone 2 via line 4. The cracked products may be cooled by indirect heat exchange or through contact with a quench medium introduced via line 5. If desired, the cracked products may be passed directly to a fractionation facility via line 6.

In the cracking operation portion of the hydrocarbon feed stock is converted to coke materials. The instant melt compositions suspend the coke by-product within the melt. The coke materials are removed from the melt by a gasification step involving contacting the coke containing melt with an oxidizing gas. In the process of the present invention, the molten media that contains suspended carbonaceous material is withdrawn from cracking zone 2 by way of line 7 and introduced to gasification zone 8. Preferably, a vapor lift is used to circulate the melt between the cracking zone and the gasification zone. Within gasification zone 8, the coke-containing molten media 9 is contacted with a reagent introduced into the gasification zone 8 via line 10. Preferably the reagent is elemental oxygen (or a gas stream containing elemental oxygen), steam or carbon dioxide. During contact with the gasifying reagent, the temperature within the gasification zone may be brought to about 2,000.degree.F.

During gasification, the coke or carbonaceous material contained in the melt is combusted and the gasification products carried overhead via line 11. The chemical composition of the overhead gaseous effluent is dependent on the type of gasifying reagent employed. When oxygen or an oxygen-containing gas is employed, only a minor proportion of the total gaseous effluent is made up of sulfur-bearing materials. When the ratio of alkaline reagent, calculated on the basis of the oxides thereof, to glass-forming oxide exceeds certain minimum levels, the resulting oxygen gasification products are predominantly sulfur free (containing below about 500 vppm, generally below 200 vppm sulfur constituents). This result is believed to be achieved because the sulfur oxides formed during gasification react with a portion of the alkaline reagent constituents of the melt to form metal sulfites or sulfates. Upon recycle of the gasified melt to the cracking zone via line 12, the inorganic sulfur-bearing materials are believed to be reduced to the corresponding sulfides due to the renewed presence of carbonaceous material in the melt. When steam is used as the gasifying reagent, the sulfur impurities contained in the melt within the gasification zone 8 are not converted to sulfur oxides and are not absorbed or reacted with the melt constituents but, rather, are converted to hydrogen sulfide which passes overhead via line 11.

During continued use the initial charge of melt material will become contaminated with larger and larger amounts of sulfur and ash-forming impurities. Accordingly, to maintain the melt in the desired active condition, a portion of the contaminated melt must be withdrawn from the system and replaced with fresh melt or, alternatively, reconditioned and returned to the system. One technique for reconditioning the contaminated melt is depicted in the FIGURE. Specifically, a minor quantity of contaminated melt material is withdrawn from line 7 and passed to a sulfur recovery zone 14 wherein it is contacted with carbon dioxide and steam that are introduced via line 15. Typically the melt 16 contained within zone 14 is treated with the carbon dioxide/steam reagents at temperatures in the range of from about 800.degree. to 1,800.degree.F. Provided that the bulk of the sulfur contaminants present in the melt are in the form of sulfides, contacting with the steam/carbon dioxide mixture will convert the sulfide ion to hydrogen sulfide which is removed from the treating zone via line 17. If the bulk of the sulfur sent to zone 14 is not in a metal sulfide form, it is necessary, for maximum sulfur removal, to reduce the sulfur present in the melt to a sulfide form in a reducing zone located prior to zone 14.

After treatment in zone 14, the molten media having reduced sulfur content is withdrawn via line 18 and returned to the system via line 19. A portion of the treated effluent in line 19 may be withdrawn from the system via line 20 for treatment for the removal of ash constituents. The resulting sulfur-free, ash-free melt may be returned to the system.

In addition to the melts becoming contaminated with sulfur materials and ash constituents, a portion of the alkaline reagent constituents of the melt may be converted to the corresponding carbonates through reaction with carbon dioxide generated during the gasification portion of the integrated process. The equilibrium carbonate concentration of the melt will generally increase as the mole ratio of alkaline reagent to glass-forming oxide increases and as the molecular weight of the cation constituent of the alkaline reagent increases (a melt containing potassium will absorb more carbon dioxide than a melt containing sodium). The carbonate concentration in the molten media is preferably maintained at a minimum level and preferably comprises less than about 30 wt. percent of the total melt, more preferably about 20 wt. percent and most preferably, below about 15 wt. percent of the total melt. Since the alkali and/or alkaline earth constituents of the melt are at least partially converted to sulfates, sulfites, sulfides and carbonate materials, the mole ratio of alkaline reagent (oxides, hydroxides and mixtures thereof) to glass-forming oxide will decrease as the sulfur and carbonate compounds are formed. Accordingly, it may be necessary to periodically add additional amounts of alkaline reagent to the melt in order to maintain the desired mole ratio of alkaline reagent to glass-forming oxide in the melt.

This invention will be further understood by reference to the following examples.

EXAMPLE 1

A heavy hydrocarbon feedstock, specifically a bitumen exhibiting physical properties as shown in Table II, was introduced by means of a pump at a rate of about 1.0 gram per minute to a 3/4 inch schedule 40 pipe 6 inches long preheat section followed by a 2 inches schedule 40 SS pipe 12 inches long reaction zone containing a molten medium consisting of a sodium metaphosphate melt, i.e., containing sodium oxide as the alkaline reagent in equimolar amounts with phosphorous pentoxide. The conversion zone was 2 inches in diameter and 10 inches in length and was placed in a Lindberg furnace. The melt temperature was measured by a thermocouple inserted into a thermowell position in the center of the molten medium connected to a portable pyrometer. An inert diluent, namely steam, in the amount of 1.0 gram per minute was introduced into the reaction zone. The effluent gases were cooled in a water condenser and noncondensable gases were passed directly to a gas chromatograph for analysis. The test results are reported below.

TABLE II ______________________________________ PHYSICAL PROPERTIES OF BITUMEN FEEDSTOCK ______________________________________ Feedstock Bitumen ______________________________________ Gravity, .degree.API 7.1 Elemental Analysis, Wt. % Carbon 83.1 Hydrogen 10.59 Sulfur 4.30 Nitrogen 0.50 Oxygen -- H/C Atomic Ratio 1.517 CCR, Wt. % 15.0 Yield on Crude, LV% 100.0 Distillation, Wt. % C.sub.5 -430.degree.F. -- 430-650.degree.F. 9.8 650-1050.degree.F. 35.9 1050.degree.F.+ 54.3 Metals, ppm Fe 1500 V 178 Ni 82 ______________________________________

TABLE III __________________________________________________________________________ CONVERSION OF A HEAVY HYDROCARBON FEEDSTOCK IN A STABLE, REGENERABLE MOLTEN MEDIUM __________________________________________________________________________ 1g/min Feed Rate; 10" Melt Depth; NaPO.sub.3 Melt Melt Temp., .degree.F. 900 950 1000 1050 1100 1150 1200 __________________________________________________________________________ Gas Yield, wt.% C.sub.3 .sup.- 1.7 1.4 1.6 3.7 5.8 7.1 9.0 C.sub.4 0.5 0.3 0.3 0.8 1.2 1.6 2.9 Total 2.2 1.7 1.9 4.5 7.0 8.7 11.9 Liquid Yield, LV%* C.sub.5 /430.degree.F 7.7 7.5 8.2 8.0 8.1 10.3 11.1 430/650.degree.F 20.2 23.4 21.9 24.7 23.2 21.5 24.1 650/1050.degree.F 50.9 50.7 52.1 49.3 47.0 41.9 37.2 1050.degree.F+ 10.9 8.3 7.8 5.7 6.4 7.7 4.5 975.degree.F+ 19.1 -- 15.7 -- 12.8 -- 8.7 Total 89.7 89.9 90.0 87.8 84.7 81.4 76.9 Liquid Yield, wt.% 87.4 87.4 87.3 85.3 82.9 80.0 76.4 Total Liquid Inspections .degree.API Gravity 13.7 14.1 14.3 14.0 12.9 12.4 11.5 Sulphur, wt.% 4.2 3.8 4.3 4.3 3.7 4.5 4.5 Nitrogen, wt.% 0.27 -- -- 0.27 0.28 0.20 0.24 CCR, wt.% -- -- -- 6.2 6.2 -- 6.6 Fe, wppm 4 4 2 1 2 2 2 Ni, wppm 12 12 13 20 19 18 25 V, wppm 20 19 31 39 40 35 35 Coke Yield, wt.% 10.4 10.9 10.8 10.1 10.2 11.3 11.7 Sulphur, wt.% 8.0 7.1 8.2 7.3 6.9 6.5 6.4 Sulphur Balance 106 97 106 101 100 99 95 975.degree.F+ Conversion, LV% 66 -- 72 -- 77 -- 84 __________________________________________________________________________ * GC Distillation

As can be seen from the results as shown in Table III, the conversion of a heavy hydrocarbon feedstock in a molten medium of the instant invention results in extremely high conversions to liquid hydrocarbon products.

EXAMPLE 2

A hydrocarbon feedstock comprising a crude oil having the characteristics shown in Table IV was introduced into a sodium metaphosphate molten salt reactor in the same manner as was employed in Example 1. The results of converting the crude oil feedstock into predominantly liquid products by the process of the instant invention is shown in Table V.

TABLE IV ______________________________________ PHYSICAL PROPERTIES OF CRUDE OIL FEEDSTOCK ______________________________________ Feedstock Crude Oil Feedstock ______________________________________ Gravity, .degree.API 10.2 Elemental Analysis, Wt. % Carbon 83.1 Hydrogen 10.90 Sulfur 4.30 Nitrogen 0.45 Oxygen -- H/C Atomic Ratio 1.561 CCR, Wt. % 12.0 Yield on Crude, LV % 100.0 Distillation, Wt. % C.sub.5 -430.degree.F. 6.1 430-650.degree.F. 14.8 650-1050.degree.F. 29.0 1050.degree.F.+ 50.0 Metals, ppm Fe 384 V 155 Ni 47 ______________________________________

TABLE V ______________________________________ MELT CRACKING OTHER FEEDS ______________________________________ 1g/min Feed Rate; 10" Melt Depth Feed Heavy Crude Oil* ______________________________________ Melt Temperature, .degree.F. 900 1000 1100 Gas Yield, wt.% C.sub.3.sup.- 1.8 2.4 3.0 C.sub.4 0.3 0.5 1.7 Total 2.1 2.9 4.7 Liquid Yield LV, % C.sub.5 /430.degree.F 7.7 8.3 11.3 430/650.degree.F 26.6 26.5 27.8 650/1050.degree.F 49.5 48.8 45.1 1050.degree.F+ 8.9 8.2 6.3 975.degree.F+ 15.6 15.9 13.2 Total 92.7 91.8 90.5 Liquid Yield, wt. % 88.2 87.5 85.9 Total Liquid Inspections .degree.API Gravity 17.3 16.5 17.6 Sulphur, wt.% 3.6 3.7 3.5 Nitrogen, wt.% 0.15 0.24 0.11 Fe, wppm 4 3 1 Ni, wppm 8 13 14 V, wppm 20 41 34 Coke, wt. % 9.6 9.6 9.6 975.degree.F+ Conversion, LV% 70 69 74 ______________________________________ *NaPO.sub. 3 melt

As can be seen from the results as shown in Table V, the cracking of a crude oil feedstock in the molten media system of the instant invention likewise results in high conversion to materials boiling up to about 950.degree.F.

EXAMPLE 3

This example shows the high conversions that are obtained by the process of the instant invention as compared with conventional methods of upgrading heavy hydrocarbon feedstocks by employing mild pyrolysis techniques such as visbreaking and hydrovisbreaking. Table VI shows the typical results obtained when the same heavy hydrocarbon feedstocks employed in Examples 1 and 2, respectively, namely a heavy hydrocarbon bitumen and a crude oil feedstock, are subjected to conventional visbreaking and hydrovisbreaking conversion processes.

TABLE VI ______________________________________ TYPICAL HEAVY FEED CONVERSION PROCESS YIELDS ______________________________________ Process Visbreaking Hydrovisbreaking Feed Crude Crude Bitumen ______________________________________ Temperature, .degree.F. 855 798 827 -Residence Time 7 min. -- -- Pressure, psig 200 800 1500 LHSV -- 1.0 1.0 Gas Rate SCF H.sub.2 /B -- 4000 4000 Gas Yield, Wt. % C.sub.1 /C.sub.4 0.0 0 2.6 Liquid Yield, LV % C.sub.5 /300.degree.F. 4.3 7.6 7.8 300/650.degree.F. 36..2 42.3 35.7 650/975.degree.F. 29.1 29.8 34.7 975.degree.F.+ 32.1 22.5 27.3 Coke, Wt. % -- -- -- Conversion, LV % 975.degree.F.+ 33.5 53.6 50.5 ______________________________________

As can be seen from the results as shown in Table VI, converting a heavy hydrocarbon feedstock by the molten media system of the instant invention (Examples 1 and 2) results in significantly higher conversions to predominantly liquid hydrocarbon products while producing approximately 10 weight percent coke. However, as discussed above, the carbonaceous materials, i.e., coke, which are formed during the conversion process of the instant invention can be gasified with a gasifying reagent as is shown in the following example.

EXAMPLE 4

This example indicates the excellent carbon gasification rates that are obtainable in accordance with the instant invention when carbonaceous materials present in the molten melts of the instant invention are contacted with air as the oxygen-containing gas stream at 1,500.degree.F. or 1,600.degree.F.

TABLE VII ______________________________________ COKE GASIFICATION WITH AIR IN VARIOUS MELTS ______________________________________ Temperature: 1500.degree. F. except Run I; Air Flow Rate: 4 STP liters/min.; 950 grams melt containing 5 wt. % (50 grams) fluid coke except Run I. ______________________________________ Carbon Oxygen Gasification Conver- Rate (lb./ Run Melt sion(%) ft..sup.3 /hr.) ______________________________________ A 0.53 Li.sub.2 O - 0.47 K.sub.2 O - B.sub.2 O.sub.3 60 1.8 B 1.4 Na.sub.2 O - 0.05 TiO.sub.2 - V.sub.2 O.sub.5 58 1.6 C 0.7 Li.sub.2 O - 0.3 K.sub.2 O - MoO.sub.3 52 1.6 D 2Na.sub.2 O - B.sub.2 O.sub.3 45 1.5 E 0.48 Li.sub.2 O - 0.52 Na.sub.2 O - B.sub.2 O.sub.3 33 1.1 F 0.52 Li.sub.2 O - 0.48 Na.sub.2 O - WO.sub.3 17 1.0 G 1.4 Li.sub.2 CO.sub.3 - K.sub.2 O.sub.3.sup.(1) 14 0.4 H 1.3 LiCl - KCl.sup.(2) 32 0.2 I 0.8 Li.sub.2 O - 1.2 K.sub.2 O - P.sub.2 O.sub.5.sup.(3) 53 3.3 ______________________________________ .sup.(1) Run conducted at 1250.degree.F. to avoid excessive decomposition of the melt. .sup.(2) Run conducted at air flow rate of 1 STP liters/min. as LiCl-KCL melt volatilizes. .sup.(3) 480 g. melt, 1600.degree.F., 20 g. fluid coke.

As can be seen from the results as shown in Table VII, the molten media of the instant invention (Runs A through F and I) which contain glass-forming oxide(s) in combination with an alkali metal oxide promote the rapid gasification of the carbonaceous materials present in said melts, which gasification permits facile regeneration of the melt after the melt has been employed as the cracking medium for a hydrocarbon feedstock, as described in Example 1.

The molten medium employed in Run G could not be conducted at the temperatures employed in Runs A through F in view of the fact that this particular molten medium, at such temperature, evolves carbon dioxide. Likewise, the particular molten media employed in Run H could not be conducted at the air flow rate employed for Runs A through F in view of the fact that, at such air flow rates, there occurs a significant loss of the molten media from the reactor due to volatilization of the melt.

EXAMPLE 5

This example shows that steam may also be employed in order to gasify carbonaceous materials present in the molten medium of this invention.

TABLE VIII ______________________________________ COKE GASIFICATION WITH STEAM IN VARIOUS MELTS ______________________________________ Temperature: 1700.degree.F.; Steam Flow Rate: 0.5 grams/min. 450 Grams of melt containing 5 wt. % (50 grams) Fluid Coke Steam Carbon Conver- Gasification sion Rate (lb./ Run Melt (%) ft..sup.3 /hr.) ______________________________________ A 0.53 Li.sub.2 O - 0.47 K.sub.2 O - B.sub.2 O.sub.3 87 1.8 B 0.48 Li.sub.2 O - 0.52 Na.sub.2 O - B.sub.2 O.sub.3 69 1.3 C 0.7 Na.sub.2 O - V.sub.2 O.sub.5 55 0.8 D 0.52 Li.sub.2 O - 0.48 Na.sub.2 O - WO.sub.3 41 1.7 E Na.sub.2 O - 2B.sub.2 O.sub.3 27 0.5 F 1.4 Na.sub.2 O - V.sub.2 O.sub.5 13 0.2 G 2Na.sub.2 O - B.sub.2 O.sub.3 12 0.2 ______________________________________

Table VIII indicates that steam is effective as a gasification reagent; however, it is noted that in order to obtain a gasification rate equivalent to those obtained when air is employed as the gasification reagent (Run A of Example 4), higher gasification temperatures are required. Accordingly, employing gasification temperatures higher than 1,700.degree.F. would likewise increase the gasification rates exhibited by the molten media in Runs E through G.

EXAMPLE 6

A series of tests were conducted to demonstrate the efficacy of melts containing boron oxide. For comparison purposes, another series of runs were conducted wherein the melt employed was composed of alkali metal carbonate materials. The initial alkaline reagent portion of the boron-containing melt was composed of about 43 mole percent lithium as lithium hydroxide, 31 mole percent sodium as sodium hydroxide, and 26 mole percent potassium as potassium hydroxide. Sufficient boron oxide was added to the melt to bring the molar ratio of alkali compounds on an oxide basis to boron oxide to 2.5. The hydroxides/boron oxide mixture was heated in a graphite-lined reactor to a temperature ranging from 1,500.degree. to 1,600.degree.F. over a period of from 3-4 hours until a homogeneous melt was secured. Thereafter the melt was solidified by cooling, and 2,000 grams of melt particles were introduced into a graphite-lined reactor that was equipped with a stirrer and means for introducing feedstock and means for withdrawing liquid and gaseous product materials.

In each test run, 600 grams of feedstock comprising a heavy Arabian residual material having an initial boiling point at atmospheric pressure of about 980.degree.F. was continuously introduced into the reaction zone which was maintained at a temperature of about 1,000.degree.F. over a forty minute period. The feed material exhibited an API gravity of 4.6.degree., a Conradson carbon residue number (CCR) of 21 wt. percent and contained about 0.5 weight percent nitrogen, 4.8 weight percent sulfur and 280 ppm metals. The feed material was introduced into the bottom of the reactor through the feed inlet and was brought into intimate contact with the stirred melt. Product materials were continuously bled from the top of the reactor and the liquid products condensed and fractionated for subsequent analysis. The residence time of the product materials within the reaction zone varied from an average of about 20 minutes for coke materials to several seconds for lighter products.

The carbonate melt utilized in the comparative test runs was composed of about 43 mole percent lithium carbonate, 31 mole percent sodium carbonate and 26 mole percent potassium carbonate. The melt was prepared by blending the three components in the reactor. The test runs in which the carbonate melt was employed were conducted in the same manner as the experiments wherein the boron oxide containing melt was used.

The results of the experiments are set forth in Table IX below. The range of values presented are representative of results secured from a number of experiments. The relatively wide range of results can be explained by the difficulty encountered in maintaining constant residence times in all of the experiments.

TABLE IX ______________________________________ Product Properties Boron Oxide Melt Carbonate Melt ______________________________________ C.sub.5 /430.degree.F. Naphtha Yield, Once-through (wt. % on feed) 5-15 Gravity, .degree.API 50-55 S, wt. % 0.2-0.6 N, wt. % 0.02-0.03 Bromine No. 70-90 Aniline Point, .degree.F. 95-105 430.degree.F./980.degree.F. Gas Oil Yield, Once-through (wt. % on feed) 20-40 30-40 Gravity, .degree.API 22-28 S, wt. % 2-3 2.5-3.5 N, wt. % 0.1-0.2 CCR, wt. % <0.05 980.degree.F.+ Product Yield, Once-through (wt. % on feed) 15-40 Gravity, .degree.API 12-16 S, wt. % 3-4 3.5-4.5 N, wt. % 0.2-0.3 CCR, wt. % 2-10 Metals (Fe, V, Ni) ppm 7-30 Coke Yield, Once-through (wt. % on feed) 20-35 20-25 S, wt. % 1-1.5 4.5-5.5 ______________________________________

As shown in the above table, the boron oxide-containing melts serve as efficient means for the cracking of heavy petroleum residual materials. The heavier products obtained from the process contained relatively small amounts of sulfur and metals. This indicates that the melt served to partially desulfurize the feedstock materials and diminish metal contaminants concentrations. The data also shows that the boron oxide containing melt was at least equivalent in performance to the carbonate based melt. In particular, the 980.degree.F.+ product obtained with the use of the boron oxide-containing melt contains significantly less sulfur than similar products secured with the carbonate melt. Similarly, the coke obtained with the boron oxide melt was substantially sulfur-free in comparison to the coke obtained utilizing the carbonate melt.

Claims

What is claimed is:

1. A process for converting a heavy hydrocarbon feedstock to lighter hydrocarbon materials which comprises contacting said feedstock with a regenerable molten medium containing an alkaline reagent selected from the group consisting of alkali metal oxides, hydroxides and mixtures thereof, and alkali metal oxides, hydroxides and mixtures thereof in combination with alkaline earth metal oxides, hydroxides and mixtures thereof and a glass-forming oxide wherein the mole ratio of the alkaline reagent, expressed as the oxide thereof, to the glass-forming oxide is about 1.5 to about 3 at a temperature in the range of from about the melting point of said medium to less than about 1,200.degree.F. for a time sufficient to form lighter hydrocarbon materials.

2. The process of claim 1 wherein the temperature of the molten medium is maintained in the range of from about 800.degree. to less than about 1,200.degree.F.

3. The process of claim 2 wherein said glass-forming oxide is selected from the group consisting of oxides of boron, phosphorus, vanadium, silicon, tungsten, and molybdenum.

4. The process of claim 2 wherein said glass-forming oxide is boron oxide.

5. The process of claim 1 wherein said molten medium is regenerated after contact with said hydrocarbon feedstock by contacting said molten medium with oxygen, steam, carbon dioxide and mixtures thereof at a temperature in the range of from above about the melting point of said medium to about 2,000.degree.F.

6. A process for converting a heavy hydrocarbon feedstock to lighter hydrocarbon materials which comprises contacting said heavy hydrocarbon feedstock with a regenerable molten medium containing an alkaline reagent selected from the group consisting of alkali metal oxides, hydroxides and mixtures thereof and alkali metal oxides, hydroxides and mixtures thereof in combination with alkaline earth metal oxides, hydroxides and mixtures thereof and a glass-forming oxide selected from the group consisting of oxides of boron, phosphorus, vanadium, silicon, tungsten, and molybdenum, wherein the mole ratio of the alkaline reagent, expressed as the oxide thereof, to the glass-forming oxide is in the range of from about 1.5 to about 3, at a temperature in the range of from about 800.degree. to less than about 1,200.degree.F. to form predominantly liquid hydrocarbon products and carbonaceous materials and thereafter gasifying said carbonaceous materials formed during said conversion process by contacting said molten medium containing said carbonaceous materials with oxygen, carbon dioxide, steam or mixtures thereof at a temperature in the range of from about the melting point of said medium to about 2,000.degree.F.

7. The process of claim 6 wherein the temperature of the molten medium during contact with heavy hydrocarbon feedstock is maintained in the range of from about 800.degree. to about 1,100.degree.F.

8. The process of claim 7 wherein at least a portion of said heavy hydrocarbon feedstock boils above about 650.degree.F. at atmospheric pressure.

9. The process of claim 8 wherein said glass-forming oxide is boron oxide.

10. The process of claim 9 wherein said alkaline reagent is an alkali metal hydroxide, an alkali metal oxide or mixture thereof.

11. The process of claim 10 wherein the mole ratio of said alkaline reagent, calculated on the basis of the oxide thereof, to boron oxide is in the range of from about 2.2 to about 2.7.

12. The process of claim 11 wherein said gasifying reagent is a gas stream containing from about 10 to about 25 wt. percent oxygen.

13. The process of claim 12 wherein said gas stream is air.

14. The process of claim 11 wherein said gasifying reagent is steam.

15. The process of claim 6 wherein said glass-forming oxide is a boron oxide.

16. The process of claim 6 wherein said glass-forming oxide is an oxide of phosphorus.

17. The process of claim 6 wherein said molten medium is regenerated at a temperature in the range of from about 1,000.degree.F. to about 1,800.degree.F.